Conventional Cellular systems use base stations (commonly referred to as cell-sites) which cover small geographical areas (referred to as cells). Several cell-sites are connected to a master controller called the Mobile Telephone Switching Office (MTSO). The connection between the MTSO and a cell-site is usually by T1 lines which carry voice traffic as well as a data link. The MTSO is responsible for control of the cell-sites as well as providing an interface connection to the Public Switched Telephone Network (PSTN).
The service area that a cell-site covers is generally on the order of square miles and the transmitters of the cell-sites generally radiate about 500 Watts effective power.
In addition to voice channels each cell-site is provided with one special setup channel utilized for communicating control information between mobile radiotelephone units and the cell-site. When a mobile radiotelephone unit is turned on it scans the setup channels and locks onto the strongest channel. This usually results in the mobile radiotelephone unit selecting the nearest cell-site.
Current mobility management, allowing mobile radiotelephones to switch serving cell-sites, is carried out by using a data link through the MTSO to transfer mobility management messages from one cell-site to another. Current channel assignment and neighbor lists must be "RF engineered" before the system is placed into service.
In a mobile-originated call the mobile radiotelephone unit seizes the dominant setup channel and sends a message to the cell-site requesting service. The cell-site passes this information back to the MTSO which decides if the call should go through. It determines if there are available facilities (radio channel units, facilities to the PSTN, enough signal strength etc.) and if the user has dialed a valid directory number. The MTSO then sends a message to the mobile radiotelephone unit (via the forward control channel of the cell-site) and assigns a voice channel to it. Upon the cell-site determining that the mobile has tuned to the correct voice channel, the cell-site sends a voice confirmation message to the MTSO where any remaining switching tasks are completed.
The cellular network provides mobility to the user through a mechanism referred to as "handoff". Cell-sites which are geographically adjacent are considered to be neighbor cell-sites. These are the cell-sites that a call can be transferred to as a mobile radiotelephone unit moves past the current cell-site boundary. This transferring of a call from one cell-site to another is called a handoff. The translation paramenters, which specify which cell-sites are to be considered in a handoff process, are included in a table called the "neighbor list". The neighbor list for each cell is constructed during the "RF engineering" stage by the service provider.
During a call the cell-site will send a message to the mobile radiotelephone unit asking it to make an RSSI measurement on a particular channel. The cell-site selects the channel the mobile uses to make this measurement. This selection is based on the information contained in its neighbor list for that particular cell-site. The mobile reports this information back to the cell-site which stores that information for later use. When the RSSI level drops below a predetermined level the cell-site can then make the decision of whether to hand the call off to another cell-site based on the RSSI levels of neighboring cell setup channels reported by the mobile. If the decision is made to handoff the call, one cell-site communicates to another cell-site over the data links using a wireline connection between themselves and the MTSO.
A new version of wireless radiotelephone service, commonly identified as personal communication networks (PCN) similarly uses a localized base station or radio port communication sites much smaller in service area than a cell-site and analogous to the microcell to radiate and provide radiotelephone service within small limited local areas. PCN is normally dedicated only to a small local area of service and is not configured in a radiotelephone communication system as pan of a frequency reuse wide area pattern. Typically these radio ports are directly interconnected with the landline telephone network and do not provide for hand-off from one radio port to another.